Absolute-type rotary encoders are widely used for an input operating section of electronic devices to control various functions of the electronic devices.
FIG. 10 is a cross-sectional view of conventional absolute-type rotary encoder 500. In rotary encoder 500, operating knob 2 retained rotatably to main body 1 protrudes upward from main body 1. Main body 1 includes case 3 made of insulating resin, and bearing 4 disposed above case 3. Bearing 4 includes cylinder 4A protruding upward, and flange 4B provided at a base of cylinder 4A. Flange 4B has a shape substantially identical to that of an upper surface of case 3. Flange 4B is disposed on the upper surface of case 3. Metallic cover 5 covers flange 4B. Leg 5A of cover 5 is crimped to be fixed on a lower surface of case 3, thereby fixing bearing 4 unitarily with case 3. Operating knob 2 upwardly protrudes through cylinder 4A of bearing 4 and is rotatably held on an inside wall of cylinder 4A.
Case 3 has a recess opening upward. The recess has substantially a circular shape in view from above. Contact pattern 6 for the absolute-type encoder is provided on a bottom surface of the recess. Rotatable conductor 7 having elasticity is fixed by crimped onto a lower surface of a circular plate disposed under operating knob 2. Rotatable conductor 7 is a spring made of conductive material, such as thin sheet metal, with resiliency.
FIG. 11 is a plan view of rotatable conductor 7. Rotatable conductor 7 has contact fingers 8 and 9A to 9D. Contact fingers 8 and 9A to 9D elastically contact predetermined positions on the bottom surface of the recess.
Recesses and protrusions extending radially are formed on the upper surface of the circular plate of operating knob 2. A click spring is fixed at a lower section of bearing 4 bycrimping. Upon rotating, operating knob 2 causes the recesses and the protrusions to elastically contact the click spring, producing the operator a click feel by a predetermined rotation angle.
An operation of rotary encoder 500 will be detailed below. FIG. 12 is a schematic view of rotary encoder 500 for illustrating contact pattern 6 and positions of contact fingers 8 and 9A to 9D. FIG. 13 is a schematic view of rotary encoder 500 for illustrating positional relation between contact pattern 6 and contact fingers 8 and 9A to 9D according to the rotation of operating knob 2. FIG. 14 shows output codes corresponding to angular positions of operating knob 2 of rotary encoder 500.
Upon operating knob 2 rotating, contact fingers 8 and 9A to 9D of rotatable conductor 7 are connect and disconnect with contact pattern 6 in the recess and provide contact pattern 6 with a predetermined a contact/non-contact state, consequently output predetermined output signals according to angular positions of operating knob 2 from signal terminals 12A to 12D that are led out of a side surface of case 3.
Case 3 is form by insert molding wiring board 13 such that an upper surface of wiring board 13 is exposed at the bottom surface of the recess of case 3. Predetermined contact pattern 6 is provided on the upper surface of wiring board 13 exposed at the recess.
Contact pattern 6 includes common contact 14 positioned at a center of the recess and signal contacts 15A to 15D surrounding common contact 14. Common contact 14 has a common potential and has an annular shape with a predetermined width. Signal contacts 15A to 15D are electrically independent of each other, and have substantially horseshoe shapes that extend in the circumferential direction so as to surround common contact 14 located at the center. As shown in FIG. 12, contact pattern 6 disposed on the bottom surface of the recess includes five circular tracks, track 514 and tracks 515A to 515D. Circular tracks 514, 515A to 515D are concentric circles. Common contact 14 and signal contacts 15A to 15D extend along the tracks. Signal contacts 15C, 15D, 15A, and 15B are arranged in this order radially away from common contact 14 located at the center of the recess. Each of signal contacts 15A to 15D has a wide part with a large width in the radial direction and a narrow part with a small width in the radial direction at a predetermined angular position.
Common contact 14 and signal contacts 15A to 15D are led out with wiring patterns disposed on wiring board 13 to an outer edge of wiring board 13. Common terminal 11 and signal terminals 12A to 12D made of metal plates are led out of the side surface of case 3. Common contact 14 and signal contacts 15A to 15D are connected to common terminal 11 and signal terminals 12A to 12D, respectively.
The wiring patterns disposed on the upper surface of wiring board 13 is covered with a resist material so as not to expose the wiring patterns to the outside. That is, only common contact 14 and signal contacts 15A to 15D of contact pattern 6 are exposed to an upper surface of wiring board 13 at the bottom surface of the recess of case 3.
Contact fingers 8 and 9A to 9D of rotatable conductor 7 are arranged along a diameter of the circular shape of the recess of case 3. FIG. 12 schematically illustrates positions of contact fingers 8 and 9A to 9D of rotatable conductor 7. Contact fingers 8, 9C, 9D, 9A, and 9B are arranged on circular tracks 514, 515C, 515D, 515A, and 515B of common contacts 14, 15C, 15D, 15A, and 15B, respectively. An angular position of contact finger 9A disposed on circular track 515A for signal contact 15A is a reference position (i.e., at an angular position of 0 degree), contact fingers 9C and 9D are located at angular positions different from the angular position of contact finger 9A by about 180 degrees about the center of wiring board 13. Contact finger 9B is disposed at an angular position (0 degree) identical to that of contact finger 9A. Contact finger 8 contacting common contact 14 is located at an angular position different from the angular position 9A by about 180 degrees. FIG. 12 illustrates the positional relation of common contact 14 and signal contacts 14A to 14D when operating knob 2 is positioned at position No. 0 (i.e., at an angular position of 0 degree).
Upon rotating, operating knob 2 causes rotatable conductor 7 held by operating knob 2 to rotate, accordingly causing contact fingers 8 and 9A to 9D of rotatable conductor 7 to slide on common contact 14 and signal contacts 15A to 15D along circular track 514 and circular tracks 515A to 515D, respectively. Contact finger 8, sliding on common contact 14 along circular track 514 contacts an upper surface of common contact 14 along the entire circumference. Contact fingers 9A to 9D sliding on signal contacts 14A to 14D along circular tracks 514A to 514D, respectively, slide on the wide parts of signal contacts 15A to 15D while not contacting the narrow parts of signal contacts 15A to 15D, respectively. This structure allows common contact 14 to connect and disconnect with signal contacts 15A to 15D according to the angular position of operating knob 2.
In conventional rotary encoder 500, operating knob 2 is rotatable without limits. For one complete rotation of operating knob 2, an output signal is cyclically obtained at 16 angular positions (position No. 0-15). The rotation angle of operating knob 2 between adjacent angular positions is determined to 22.5°.
FIG. 13 schematically shows the positions of contact fingers 8 and 9A to 9D of rotatable conductor 7 when operating knob 2 is positioned at an angular position of position No. 1 after rotating clockwise by one position (22.5 degrees) from position No. 0 shown in FIG. 12. At position No. 1, contact finger 9A contacts signal contact 15A while contact fingers 9B to 9D do not contact signal contacts 15B to 15D, respectively. This arrangement allows signal contact 15A only to have the same potential as common contact 14, and allows signal contacts 15B to 15D to open. As a result, rotary encoder 500 outputs an output code, “0001” via signal terminals 12A to 12D.
FIG. 14 shows output codes corresponding to angular positions of operating knob 2. Rotary encoder 500 includes four signal contacts 15A to 15D and provides 4-bit output codes having first to fourth bits to allow the angular positions of position Nos. 0-15 of operating knob 2 to be detected. In FIG. 14, the first to fourth bits of the output codes correspond to the output signals output from signal contacts 12A to 12D, respectively. When signal contacts 15A to 15D contact signal terminals 12A to 12D, respectively, signal terminals 12A to 12D have the common potential. This status is represented by “1”. The status in which When signal terminals 12A to 12D do not contact signal terminals 12A to 12D is represented by “0”. In rotary encoder 500, the first bit is the least significant bit (LSB) of the output signal, and the fourth bit 4 is the most significant bit (MSB) of the output signal. For example, when operating knob 2 is located at position No. 0 shown in FIG. 12, the output code is “0000”. When operating knob 2 is located at position No. 1 shown in FIG. 13, the output code is “0001”. Upon rotating further clockwise from position No. 1 shown in FIG. 13, operating knob 2 moves consequently to positions of position Nos. 2 to No. 15.
Signal contacts 15A to 15D are connected and disconnected with contact fingers 9A to 9D at angular positions of position Nos. 2 to 15, accordingly providing the output codes corresponding to position Nos. 2 to 15 shown in FIG. 14
As described above, contact fingers 9A to 9D of rotatable conductor 7 slide on signal contacts 15A to 15D along circular tracks 515A to 515D, respectively. Contact fingers 9A to 9D are connected and disconnected with signal contacts 15A to 15D according to the angular position of operating knob 2, respectively, thereby outputting signals of the output codes according to the angular position of operating knob 2 from signal terminals 12A to 12D.
The output code is a binary number having four bits corresponding to signal terminals 12A to 12D. The output code of the four bits is a Gray code in which only one bit out of four bits changes between output codes corresponding to any pair of angular positions Nos. 0 to 15 adjacent to each other.
A conventional rotary encoder similar to rotary encoder 500 is disclosed in, for example, Japanese Patent Paid-Open Publication Nos. 10-511183 and 08-313301.